This invention relates to the production of a synthesis gas (syngas) using a partial oxidation (POX) reactor and a reforming exchanger.
Reforming of hydrocarbons is a standard process for the production of hydrogen-containing synthesis gas used for ammonia or methanol, for example. Conventional POX reactors are unpacked, free-flow, non-catalytic gas generators to which preheated hydrocarbon gas and oxygen are supplied, optionally with a temperature moderator. The partial oxidation reactor effluent is then quenched or cooled, typically to 200–300° C., optionally cleaned to remove soot, and usually further converted in high and low temperature shift converters wherein CO and steam react to form additional hydrogen and CO2. Syngas with high hydrogen content is especially desirable for ammonia or other synthesis processes where hydrogen is the main reactant from the syngas. The steam to hydrocarbon weight ratio in the POX reactor feed is generally from 0.1 to 5, the atomic ratio of oxygen to carbon in the hydrocarbon is in the range from 0.6 to 1.6, and reaction times vary from 1 to 10 seconds.
POX reactors are described, for example, in U.S. Pat. Nos. 2,896,927; 3,920,717; 3,929,429; and 4,081,253, which are hereby incorporated herein by reference in their entirety.
POX reactors produce a syngas effluent at a very high temperature prior to quenching, e.g. from 1100° to 1650° C. This means that much of the hydrocarbon feed must, in effect, be used as a rather expensive fuel to preheat feeds and generate high- or medium-pressure steam. However, the steam production is usually far in excess of plant requirements and must therefore be exported, and frequently there is little or no market for the steam.
There is a need in the art for a way to improve efficiency of hydrogen plants that use POX reactors and reduce or eliminate the steam export. It is also frequently desired to maximize or increase hydrogen production from an existing hydrogen plant; however, the POX reactor is frequently a capacity-limiting operation. POX reactors cannot easily be expanded to increase production.
The present invention addresses these needs by supplying the partially cooled POX reactor process effluent to the shell side of a reforming exchanger to provide heat for additional syngas production. Reforming exchangers used with autothermal reformers are known, for example, from U.S. Pat. Nos. 5,011,625 and 5,122,299 to LeBlanc and U.S. Pat. No. 5,362,454 to Cizmer et al, all of which are hereby incorporated herein by reference in their entirety. These reforming exchangers are available commercially under the trade designation KRES or Kellogg Reforming Exchanger System.